In a screw grinder for grinding a screw groove with the rotation axis of a whetstone inclined relative to a main spindle, the rotation axis of the whetstone is inclined relative to the main spindle by an angle equal to the lead angle of a screw groove (for example, the screw groove of a ball nut) and the whetstone having the same shape as the section shape of the screw groove is moved along the screw groove to thereby work the screw groove in an accurate shape.
In this case, instead of inclining the grinding spindle or a spindle housing supporting it, as shown in FIG. 11, the rotation axis S of a whetstone 203 is inclined according to the lead angle α of a screw groove 302 to be formed in the cylindrical inner peripheral surface 301 of a work 300 to thereby keep the axis of a quill 201 mounted in a spindle housing 250 parallel to the axis of the main spindle.
Conventionally, for example, in a spindle apparatus disclosed in the patent document 1, a flexible shaft (wire) serving as a drive shaft is disposed within an integrally structured quill and a whetstone is connected to the leading end of the flexible shaft, whereby the whetstone can be rotated around a rotation axis inclined relative to the axis of the quill.
Also, in a grinding spindle disclosed in the patent document 2, a flexible shaft is used as a drive shaft and the inclination of the leading end side of the quill can be adjusted along an arc-shaped guide rail relative to the axis of the quill.